Size of Room

• Measure the room or rooms that you need to cool. The length of the room times the width of the room will give you the total square footage of the room. If the area is less than 100 square feet or more than 150 square feet, a 5,000 BTU air conditioner will not cool the area sufficiently.
  
  

Area Location

• If the rooms are located on the shady side of the house, you can reduce the BTUs needed by 10 percent. However, if the rooms are on the sunny side of the house, you will need to increase the BTUs by 10 percent. For instance, if the room or rooms are 165 square feet but are on the shady side of the house, you can use a 5,000 BTU air conditioner. If the room or rooms are on the sunny side of the house, the area size can only be 90 square feet.
  
  

People and Room Description

• Rooms that will have more than two people in the room at one time will increase the BTUs needed to cool the room by 600 BTUs, thus reducing the square footage of the room or rooms that a 5,000 BTU unit can cool to less than 150 square feet. Air conditioners that are used to cool kitchens will increase the BTUs needed to cool the area by 4,000 BTUs, which means the area you can cool is less than 100 square feet.
  
  

Wrong Room Sizes

• A 5,000 BTU air conditioner that is used in an area larger than 150 square feet under normal conditions will not cool the room. The unit will run continually, wasting energy and leaving the room feeling sticky. Units that are used to cool rooms smaller than 100 square feet will shut off and on to cool the room but will not remove the humidity.